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Image Processing and Coding of SAR image data

TNT members involved in this project:
Prof. Dr.-Ing. Jörn Ostermann
Dr.-Ing. Ulrike Pestel-Schiller
Dipl.-Math. techn. Aron Sommer
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Synthetic Aperture Radar (SAR) is an active microwave sensor technique that has the ability to produce high-resolution SAR images of terrain. A moving platform transmits series of coherent radar chirp pulses directed sideways of the flight trajectory. Coherent addition of the echoes received from the illuminated area yields so-called 2D SAR raw data, from which, after SAR processing, 2D SAR image data are obtained.

SAR, unlike optical systems, is an active radar system and hence works in all weather conditions and at night. Therefore it has been widely applied in remote sensing and mapping.

For transmission of airborne SAR data from a platform to a receiving ground station the amount of SAR data has to be reduced to not exceed the available channel capacity. The interpretability of the SAR images at the ground station, at least within regions of interest, should not be impaired by the data rate reduction.

First investigations have shown that the processing of SAR raw data to SAR image data must take place on board the platform, in order to stay within the channel capacity limit. On-board processing therefore comprises SAR processing resulting in focused SAR image data as well as data compression. The compressed bitstream can be sent to a ground station and can be decoded into focused SAR reference images, such images which can directly be evaluated by human experts. Correspondingly, the investigated system comprises two tasks:
1. Generating well-focused SAR image data automatically
2. Efficient coding of the SAR image data
3.  Usability-Based SAR System Assessment:

1. SAR imaging assumes that the platform, which can be an airplane or a satellite, moves on a straight line at constant velocity. Real flight paths differ from that assumption which, if uncompensated, create image artifacts. Compensation based on motion information is conceptually possible. But motion parameters as obtainable from on-board GPS (Global Positioning System) and INS (Inertial Navigation System) often lack accuracy, so that so called autofocus algorithms have to be used in order to obtain well-focused images. Our autofocus approach is based on the Phase-Gradient-Algorithm, which estimates and corrects the phase error produced by the residual motion errors.

2. For an efficient coding of the focused SAR image data, a pre-processing has been developed, which dynamically converts the focused SAR image data into reference image data. Current research focuses on the data rate reduction required to transmit the reference image data within the limited channel capacity and without any loss of important image content. Because of the similarity of the reference SAR images to electro-optical images, the investigated SAR-codec is based on a standardised image codec extended by SAR specific reduction techniques.

3. Human evaluation of SAR images as an indirect means for usability-based assessment of the SAR systems from which the images arose, is time-consuming and costly. An assessment system is developed which aims at finding digital signal processing algorithms to simulate, complement and partly replace the human evaluation of SAR images.

 

Show recent publications only
  • Journals
    • Martin Kirscht
      Detection and imaging of arbitrarily moving targets with single-channel SAR
      IEE Proceedings on Radar, Sonar and Navigation, pp. 280-285, October 2002
  • Conference Contributions
    • Aron Sommer, Jörn Ostermann
      Flight Path Reconstruction From SAR Images and Spotlight SAR Data
      11th European Conference on Synthetic Aperture Radar, 11th European Conference on Synthetic Aperture Radar, pp. 1 - 5, Hamburg, June 2016
    • Aron Sommer, Jörn Ostermann
      Explicit Motion Compensation for Backprojection in Spotlight SAR
      17th International Radar Symposium, 17th International Radar Symposium, pp. 1 - 4, Krakow, May 2016
    • Aron Sommer, Minh Phuong Nguyen, Jörn Ostermann
      Comparison of Omega-K and backprojection regarding spatial resolution for squinted spotlight SAR with motion errors
      Synthetic Aperture Radar (APSAR), 2015 IEEE 5th Asia-Pacific Conference, Synthetic Aperture Radar (APSAR), 2015 IEEE 5th Asia-Pacific Conference, pp. 143 - 147, Singapore, September 2015
    • Minh Phuong Nguyen
      Range Cell Migration Correction for Phase Error Compensation of Highly Squinted SAR
      10th European Conference on Synthetic Aperture Radar, Berlin, June 2014
    • Ulrike Pestel-Schiller
      Coding of SAR Image Data for Data Compression
      10th European Conference on Synthetic Aperture Radar, Berlin, June 2014
    • Minh Phuong Nguyen, Samer Ben Ammar
      Second Order Motion Compensation for Squinted Spotlight Synthetic Aperture Radar
      Asia-Pacific Conference on Synthetic Aperture Radar (APSAR), Tsukuba, Japan, September 2013
    • Minh Phuong Nguyen
      Refined Motion Compensation for Highly Squinted Spotlight Synthetic Aperture Radar
      9th European Conference on Synthetic Aperture Radar, pp. 738-741, Nuremberg, April 2012
    • Minh Phuong Nguyen
      Omega-K Algorithm – A Generalization for Highly Squinted Spotlight SAR Imaging with Dechirp-on-Receive
      Asia-Pacific Conference on Synthetic Aperture Radar, pp. 137-140, Seoul, Korea, September 2011
    • Ridha Farhoud
      Estimation of the Phase-Error Function for Autofocussing of SAR Raw Data
      International Radar Symposium Proc. (IRS), p. 785–790, Hamburg, Germany, September 2009
    • N. Nolte, C. Simon-Klar, S. Langemeyer, M. Kirscht, P. Pirsch
      Next generation on-board SAR processor for compact airborne systems
      Geoscience and Remote Sensing Symposium 2005, IGARSS apos;04, IEEE International, Vol. 2, pp. 1514 - 11517, September 2004
    • Martin Kirscht
      Estimation of Velocity, Shape, and Position of Moving Objects with SAR
      4th International Airborne Remote Sensing Conference and Exhibition, Ottawa, Ontario, Canada, 21-24 June 1999, 1999
    • Johanna Bolle
      Quality Assessment for SAR Raw Data Compression Methods
      International Airborne Remote Sensing Conference and Exhibition, Ottawa, Ontario, Canada, 21-24 June 1999, 1999
    • Johanna Bolle
      Coding of SAR Raw Data
      European Conference on Synthetic Aperture Radar (EUSAR"98), Friedrichshafen, Germany, 25-27 May 1998, 1998
    • Martin Kirscht
      Detection, Velocity Estimation and Imaging of Moving Targets with Single-Channel SAR
      European Conference on Synthetic Aperture Radar (EUSAR"98), Friedrichshafen, Germany, 25-27 May 1998, 1998
    • Martin Kirscht, Carsten Rinke
      3D Reconstruction of Buildings and Vegetation from Synthetic Aperture Radar (SAR) Images
      IAPR Workshop on Machine Vision Applications MVA"98, Makuhari, Chiba, Japan, 17-19 November 1998, 1998
    • Johanna Bolle
      Coding of SAR Raw Data Using Reversible Transforms
      Proceedings of the Third International Airborne Remote Sensing Conference and Exhibition, Copenhagen, Denmark, 7-10 July 1997, 1997
    • Martin Kirscht
      Detection and focused imaging of moving objects evaluating a sequence of single-look SAR images
      Proceedings of the Third International Airborne Remote Sensing Conference and Exhibition, Copenhagen, Denmark, 7-10 July 1997, pp. I-393 - I-400, 1997
    • Markus Kampmann, Ridha Farhoud
      Precise Face Model Adaptation for Semantic Coding of Videophone Sequences
      Picture Coding Symposium (PCS" 97) Berlin, Germany, 10-12 Sept. 1997, 1997
    • Martin Kirscht
      Detection and velocity estimation of moving objects in a sequence of single-look SAR images
      International Geoscience and Remote Sensing Symposium IGARSS "96, Lincoln, Nebraska, USA, May 1996, 1996